All Sky camera for LSST site.
Pachon is at West long of 70.7333, lat -30.2333
used USNO site http://aa.usno.navy.mil/data/docs/RS_OneYear.php to determine civil twilight times in UT.
Data file is here pachon_twilight.dat
broke that into one file per month, called mxx.dat with xx ranging from 01 to 12. Did
grep -v "%" pachon_twilight.dat | awk '{print $3,$2}' > m01.dat
note that this intentionally reverses the times so that sundown in column 1 and sunrise in col 2, in UT